|"Is it possible Msoft has already switched off other updates for XP?"|
No, they haven't. I just switched on an old XP system this morning that hadn't been used in almost 6 months & it almost immediately began downloading Windows updates.
If you don't have CCleaner, I suggest you download/install the Slim version, then run both the cleaner & the registry scanner. Remove everything they find. Reboot, then try manually running Windows Update from Start > All Programs menu. It may take several minutes to load so be patient.
EDIT: I see you responsed while I was typing out my response.
message edited by riider